Artificial spinal fusion implants

ABSTRACT

A spinal implant for promoting fusion between adjacent vertebrae consisting of an integral, generally rectangular member having a plurality of openings for promoting ingrowth. In the preferred embodiment, the implant has an interior enclosed chamber, accessible from the outside through an opening in one wall, and a cap for covering said opening in the wall.

This application is a continuation of application Ser. No. 08/597,539,filed Feb. 2, 1996, now abandoned, which is a continuation of Ser. No.08/462,801 filed Jun. 7, 1995 now abandoned; which is a continuation ofSer. No. 08/263,952 filed Jun. 22, 1994, now abandoned; which is acontinuation of Ser. No. 08/052,211 filed Apr. 22, 1993, now abandoned,which is a continuation of Ser. No. 07/546,849 filed Jul. 2, 1990, nowabandoned; which is continuation of Ser. No. 07/212,480, filed Jun. 28,1988, now abandoned.

BACKGROUND

The present invention relates to an artificial fusion implant to beplaced into the intervertebral space left after the removal of a damagedspinal disc.

The purpose of the present invention is to provide an implant to beplaced within the intervertebral disc space and provide for thepermanent elimination of all motion at that location. To do so, thedevice is space occupying within the disc space, rigid, self-stabilizingto resist dislodgement, stabilizing to the adjacent spinal vertebrae toeliminate local motion, and able to intrinsically participate in avertebra to vertebra bony fusion so as to assure the permanency of theresult.

At present, following the removal of a damaged disc, either bone ornothing is placed into the space left. If nothing is placed in the spacethe space may collapse which may result in damage to the nerves; or thespace may fill with scar tissue and eventually lead to a reherniation.The use of bone is less than optimal in that the bone obtained from thepatient requires additional surgery and is. of limited availability inits most useful form, and if obtained elsewhere, lacks living bonecells, carries a significant risk of infection, and is also limited insupply as it is usually obtained from young accident victims.Furthermore, regardless of the source of the bone, it is only marginalstructurally and lacks a means to either stabilize itself againstdislodgement, or to stabilize the adjacent vertebrae.

A review of all possibly related prior art will demonstrate the noveltyof the present invention.

There have been an extensive number of attempts to develop an acceptabledisc prothesis (an artificial disc).

Such devices by design would be used to replace a damaged disc and seekto restore the height of the interspace and to restore the normal motionof that spinal joint. No such device has been found that is medicallyacceptable. This group of prosthetic or artificial disc replacementsseeking to preserve spinal motion which are different from the presentinvention include:

U.S. Pat. No. 3,867,728 STUBSTAD--describing a flexible disc implant.

U.S. Pat. No. 4,349,921 KUNTZ--describing a flexible disc replacementwith rope or file like surface projections to discourage devicedislocation.

U.S. Pat. No. 4,309,777 PATIL--describing motion preserving implant withspike outer surfaces to resist dislocation and containing a series ofsprings to urge the vertebrae away from each other.

U.S. Pat. No. 3,875,595 FRONING--describing a motion preserving bladderlike disc replacement with two opposed stud like projections to resistdislocation.

U.S. Pat. No. 2,372,622 FASSIO (French)--describing a motion preservingimplant comprising complimentary opposed convex and concave surfaces.

In summary then, these and other similar devices resemble the presentinvention only in that they are placed within the intervertebral spacefollowing the removal of a damaged disc. In that they seek to preservespinal motion, they are diametrically different from the presentinvention which seeks to permanently eliminate all motion at that spinalsegment.

A second related area of prior art includes those devices utilized toreplace essentially wholly removed vertebra. Such removal is generallynecessitated by extensive vertebral fractures, or tumors, and is notassociated with the treatment of disc disease, or therefore related tothe present invention. While the present invention is to be placedwithin the disc space, these prior devices cannot be placed within thedisc space as at least one vertebra has already been removed and thereno longer remains a "disc space." Furthermore, all of these devices arelimited in that they seek to perform as temporary structural membersmechanically replacing the removed vertebra (not a removed disc) , anddo not intrinsically participate in supplying osteogenic material toachieve cross vertebrae bony fusion. Therefore, again unlike the presentinvention which provides for a source of osteogenesis, use of this groupof devices must be accompanied by a further surgery consisting of a bonefusion procedure utilizing conventional technique. This group consistingof vertebral struts rather than disc replacements would include thefollowing:

U.S. Pat. No. 4,553,273 WU--describing a turnbuckle like vertebralstrut.

U.S. Pat. No. 4,401,112 REZAIAN--describing a turnbuckle like vertebralstrut with the addition of a long stabilizing staple that spans themissing vertebral body.

U.S. Pat. No. 4,554,914 KAPP--describing a large distractible spike thatelongates with a screw mechanism to span the gap left by the removal ofa entire vertebrae and to serve as an anchor for acrylic cement which isthen used to replace the missing bone (vertebrae).

U.S. Pat. No. 4,636,217 OGILVIE--describing a vertebral strut mechanismthat can be implanted after at least one vertebra has been removed andwhich device consists of a mechanism for causing the engagement ofscrews into the vertebra above the vertebra below the one removed.

In summary then, this group of devices differs from the presentinvention in that they are vertebral replacement struts, do notintrinsically participate in the bony fusion, can only be inserted inthe limited circumstances where an entire vertebra has been removed fromthe anterior approach, and are not designed for, or intended to be usedfor the treatment of disc disease.

A third area of prior art related to the present invention includes alldevices designed to be applied to one of the surfaces of the spine. Suchdevices include all types of plates, struts, and rods which are attachedby hooks, wires, and screws. These devices differ significantly from thepresent invention in that they are not inserted within the disc space,and furthermore do not intrinsically participate in supplying osteogenicmaterial for the fusion.

Therefore, with these devices where permanent spinal immobilization isdesired an additional surgery consisting of a spinal fusion performed byconventional means or the use of supplemental methylmethacrylate cementis required. Such devices, applied to the spine but not within the discspace, would include the following:

U.S. Pat. No. 4,604,995--STEPHENS--describing a "U" shaped metal rodattached to the posterior elements of the spine with wires to stabilizethe spine over a large number of segments.

U.S. Pat. No. 2,677,369--KNOWLES--describing a metal column device to beplaced posteriorly along the lumbar spine to be held in position by itsshape alone and to block pressure across the posterior portions of thespinal column by locking the spine in full flexion thereby shifting themaximum weight back onto the patient's own disc.

Other devices are simply variations on the use of rods (e.g. Harrington,Luque, Cotrel-Dubosset, Zielke), wires or cables (Dwyer), plates andscrews (Steffee), or struts (Dunn, Knowles).

In summary, none of these devices are designed for or can be used withinthe disc space, do not replace a damaged disc, and do not intrinsicallyparticipate in the generation of a bony fusion.

Other prior art possibly related to the present invention and therefore,to be considered related to "Bony Ingrowth". Patents related to thisfeature describe either methods of producing materials or devices toachieve the same. Such patents would include:

U.S. Pat. Nos. 4,636,526 (DORMAN), No. 4,634,720 (DORMAN), No. 4,542,539(ROWE), No. 4,405,319 (COSENTINO), No. 4,439,152 (SMALL), No. 4,168,326(BROEMER), No. 4,535,485 (ASHMAN), No. 3,987,499 (SCHARBACH), No.3,605,123 (HAHN), No. 4,655,777 (DUNN), No. 4,645,503 (LIN) , No.4,547,390 (ASHMAN), No. 4,608,052 (VAN KAMPEN), No. 4,698,375 (DORMAN),No. 4,661,536 (DORMAN), No. 3,952,334 (BOKROS), No. 3,905,047 (LONG),No. 4,693,721 (DUCHEYNE), No. 4,070,514 (ENTHERLY).

However, while the present invention would utilize bone ingrowthtechnology, it would do so with conventional technology.

The final area of related prior art to be considered is that of devicesdesigned to be placed within the vertebral interspace following theremoval of a damaged disc, and seeking to eliminate further motion atthat location.

Such a device is contained in U.S. Pat. No. 4,501,269 BAGBY describingan implantable device, limited instrumentation, and a method; whereby ahole is bored transversely across the joint and then a hollow metalbasket of larger diameter is then pounded into the hole and then filledwith the bone debris generated by the drilling. The present inventiondiffers from the prior art devices in the following ways:

1. UNIVERSAL APPLICABILITY WITHOUT CONTOURING OF THE INTERSPACE. Thepresent device will fit any patient, anywhere throughout the spine, inany intervertebral disc space, and without alteration of that interspaceregardless of its natural size or shape.

2. RESTORATION AND PRESERVATION OF THE INTERSPACE. The present inventionwill restore the intervertebral space to its premorbid dimensions, anddo so by having the implant fit the space rather than having to modifythe interspace, by bone removal from the vertebrae, to accommodate theimplant.

3. END PLATE PRESERVATION. Preservation of the highly specialized weightbearing cortical bone is allowed and end plate perforation into thehighly vascular cancellous bone marrow with its attendant bleeding isavoided. Such bleeding, when it occurs, bears all the risks of bloodloss (e.g. hypoglycemic shock, transfusion transmitted diseases such ashepatitis and acquired immune deficiency syndrome, etc.), and all thecomplications arising from the resultant impaired visualization of thevital structures (e.g. nerves, blood vessels, and organs) due to suchbleeding.

4. TECHNIQUE. The technique for insertion of these implants isconsistent with the established methods of disc removal, and requiresneither specialized instrumentation nor specialized surgical technique.

5. EXTENT OF DISC REMOVAL. The extent of disc removal can be determinedby the surgeon at the time surgery and can be individualized for eachpatient.

6. NO DRILLING. No drilling is involved with the use of the presentinvention.

7. ELIMINATION OF INCORRECT IMPLANT SIZE SELECTION. In those implantsystems where a drill is used and significant bone is removed then anestimate of the implant size must first be made, and then, regardless ofthe fit, an implant at least as large as the space created by thedrilling must be utilized, regardless of the quality of that fit. Withthe present invention no significant bone is removed, and the correctsize implants are fitted directly to the interspace eliminating the needto guess at the correct implant size before the fact.

8. MODULAR DESIGN. The present implants are available in varying lengthsto accommodate the changing depths of the interspace from central tolateral. The devices are available in varying heights or are infinitelyadjustable as to the height within the physiological range. The widthsare standardized, and the various embodiments can be used in anycombination (e.g. in the lumbar spine two auto-expanding implants couldbe used in conjunction with two anchor deploying implants to completelyfill the interspace).

9. AVOIDANCE OF SIZE LIMITATIONS. Because in one embodiment the systemis modular, component parts can be inserted through a very small openinguntil a much larger implant is reconstituted completely filling theavailable interspace; and yet much larger when assembled than theopening through which the component modular sections were introduced.For example, in the lumbar spine four implants introduced one at a timeand measuring 8 mm in width, would when reconstituted within theinterspace constitute a 32 mm wide implant. Implantation of a singleimplant of those dimensions from a posterior approach in the lumbarspine. would otherwise be impossible because of the presence of thedural sac and spinal nerves.

10. THE AVOIDANCE OF INTERSPACE COLLAPSE. The device is many timesstronger than bone and will not collapse. The implantation of the deviceallows preservation of the very strong vertebral cortex, which isresistant to compression preventing the migration of the implant intothe vertebrae. The large surface area of the assembled modular implant,minimizes the load per unit area. For example, a reconstituted lumbarimplant of four modular components would have the weight distributedover approximately 8 sq. cm. per vertebral interface.

11. REMOVABILITY. Because the present invention is an interspace implantand not a "through vertebrae" cross interspace implant, removal of theimplant, should that become necessary, would not result in iatrogenicdestruction of the adjacent vertebrae.

12. SELF-STABILIZING. The implant is self-stabilizing without the use ofthreads. All of the implants are surface configured to resistdislodgement and the preferred embodiments contain active, mechanicalmeans to assure permanent anchoring.. Long term stability begins withthe above and is further enhanced by surface treating of the implant forbone ingrowth (by known conventional means) and osteogenically loadingthe implants.

13. SPINE REDUCING. Various embodiments of the present invention such asthe ones with the 180 degree opposed ratcheted surface, and theauto-expanding type, are capable of reducing a vertebral listheses (aforward or backward translation of one vertebrae upon another).

14. SPINAL STABILITY. These implants are capable of stabilizing a spinalsegment following disc removal, and do so without the use of threads(threads would be design need to violate the vertebrae themselvesextensively).

15. SAFETY. The entire procedure is performed under direct vision andwith complete visualization of the adjacent vital structures (e.g.organs, neural structures and blood vessels).

In summary then, the present invention is an interspace implant utilizedto replace a damaged disc, which unlike an artificial disc, seeks topermanently eliminate rather than to preserve spinal motion, and to doso by a bony fusion. The present invention is clearly an improvementover the prior art providing an interspace implant intrinsicallyparticipating in the fusion process, self-stabilizing, stabilizing tothe spinal segment, consistent with conventional methods of discectomy,and uniquely consistent with the preservation of the integrity of theadjacent vertebrae.

BRIEF SUMMARY OF THE PRESENT INVENTION

The present invention comprises an artificial implant, the purpose ofwhich is to participate in, and directly cause bone fusion across anintervertebral space following the excision of a damaged disc. Saidimplants are structurally load bearing devices, stronger than bone,capable of withstanding the substantial forces generated within thespinal interspace. Such devices have a plurality of macro sized openingsof 1-3 mm, which can be loaded with fusion promoting materials, such asautogenous bone, for the purpose of materially influencing the adjacentvertebrae to perform a bony bond to the implants and to each other. Theimplant casing may be surface textured or otherwise treated by any of anumber of known technologies to achieve a "bone ingrowth surface" tofurther enhance the stability of the implant and to expedite the fusion.Further, said devices are so configured and designed so as to promotetheir own stability within the vertebral interspace to resistdislodgement, and furthermore, to stabilize the adjacent vertebrae.

To use the implant of the present invention a. conventional discectomyis performed and the vertebral endplates scraped, but not perforated.The appropriately sized implants are loaded with autogenous bone andimplanted within the interspace.

For example for an anterior cervical device implantation, a shorttransverse incision is made across the front of the neck and to theright of the midline directly over the diseased disc. The platysmamuscle is split, and the sternocleidomastoid muscle with the carotidsheath is protected and retracted laterally. The esophagus, trachea andassociated midline structures are protected and retracted medially, thusexposing the anterior aspect of the cervical spine. The diseased disc isidentified and removed by conventional surgical methods. The adjacentvertebral endplates are gently scraped free of any remaining cartilageuntil diffuse fine punctuate decortication is achieved. The dimensionsof the interspace are then measured in mild distraction, and theappropriate implant selected. Cancellous bone, obtained from thepatient's iliac crest or the equivalent, is loaded into the implant. Thesafety driver is then utilized to insert the implant behind the anteriorlips of the vertebrae. The wound is then closed in the routine manner.

OBJECTS OF THE PRESENT INVENTION

It is an object of the present invention to provide for a means ofachieving interspace fusion and stabilization as a single procedure by ameans consistent with the conventional method of discectomy.

It is another object of the present invention to provide for a means ofachieving an interspace fusion and stabilization that is quicker, safer,and entails less blood loss than by any other known means.

It is another object of the present invention to provide for a means ofachieving a one stage interspace fusion and stabilization withoutsignificant violation or removal of the adjacent vertebral bone stock.

It is another object of the present invention to provide for a method ofintervertebral arthrodesis and stabilization of enhanced safety wherethe entire procedure is performed under direct vision.

It is another object of the present invention to provide for a method ofintervertebral arthrodesis and stabilization of greater simplicity andrequiring minimal specialized instrumentation or technique not alreadypossessed by those doing such procedures by conventional means.

It is another object of the present invention to provide for a modularprosthesis, allowing complimentary subunits to be inserted individuallythrough a small opening and to then be reassembled within theinterspace, so as to reconstitute an interspace occupying device muchlarger than would be insertable as a whole.

It is another object of the present invention to provide for a modularimplant system such that it is possible to precisely fit the contours ofany interspace without the need to sacrifice any vertebral bone toaccommodate the prosthesis. These and other objects of the presentinvention will be apparent from review of the following specificationsand the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top right perspective view of the implant (cervical type).

FIG. 1a is a front view of the implant of FIG. 1

FIG. 1b is a rear view of the implant of FIG. 1.

FIG. 1c is a top view of the implant of FIG. 1.

FIG. 1d is a side view of the implant of FIG. 1.

FIG. 1e is a bottom view of the implant of FIG. 1.

FIG. 2 is a side sectional view of the implant viewed along lines 2--2of FIG. 1d.

FIG. 3 is the implant FIG. 1 showing the attachment to the driver anddriver.

FIG. 4 is a front perspective view showing the implant being driven intothe disc space.

FIG. 4a is a front perspective view of the implant located in the spine.

FIG. 5 is a side view of the implant in the spine attached to thedriver.

FIG. 5a is a close up partial sectional view of the implant and driver.

FIG. 6 is a perspective view of a series of implants placed in a lumbarintervertebral space.

FIG. 6A is an alternative embodiment of a rectangular solid implant.

FIG. 7 is a side sectional view of the vertebrae and implant viewedalong lines 7--7 of FIG. 6.

FIG. 7A is a side sectional view of the vertebrae structure showing athird embodiment of the rectangular solid implant in place.

FIG. 8 is an exploded perspective view of another embodiment of thepresent invention.

FIG. 9 is a side sectional view of the vertebrae structure and implantviewed along lines 9--9 of FIG. 8.

FIG. 10 is a side sectional view of the implant of FIG. 8, in acontracted position.

FIG. 11 is a side sectional view of the implant of FIG. 10, in anexpanded position.

FIG. 12 is a perspective view of an alternative embodiment of theimplant of FIG. 9.

FIG. 13 is an alternative embodiment of a hollow rectangular solidimplant.

FIG. 14 is a cross sectional view of the hollow rectangular solidimplant of FIG. 13 viewed along lines 14--14 of FIG. 13.

FIG. 15 is an alternative embodiment of an expandable implant in itsextended position.

FIG. 16 is an expandable implant of FIG. 15 in its retracted position.

FIG. 17 is an expandable implant of FIG. 16 located in the disc space.

Referring to FIGS. 1 through 5 an implant for use in the disc space andassociated apparatus used for inserting the implant 10 is shown. Theimplant 10 is shown as a substantially rectangular hollow configuration,having a tapered forward portion.

The implant 10 has an upper surface 12 and a parallel lower surface 14.The two side walls 16 and 18 are parallel to one another and have aseries of small sized openings 20 of 1 mm-3 mm through the side walls 16and 18.

The front wall 22 is slightly convex and has a depressed portion 24 witha central threaded opening 26 for receiving the engaging end 28 of adriving member 30.

The upper surface 12 has a threaded cap 32, which has opening 33 therethrough, with a central wrench opening 34 for engagement with an allenhex key wrench wrench A of FIG. 3. The cap 32 covers the opening intothe hollow implant 10 and permits the insertion of autogenous bonematerial into the hollow portion of the implant 10. The cap 32 issurrounded by a series of small sized openings 36 of 1 mm to 3 mmpassing through the upper surface and into the central hollow portion ofthe implant 10.

The rear wall 38 is convex so as to conform to the rear of the discspace.

The driving member 30, shown in FIG. 3, comprises a substantially hollowtubular member 40 having a long internal rod 42 having a turning knob 44at one end and a threaded portion 46 at the other end for threadablyengaging the threaded opening 26 of the implant 10. The engaging end 28of the driving member 30 has a slightly convex surface to complement theslightly convex surface of the front wall 22. The engaging end 28 has anextension 48 for fitting within the depressed portion 24 on the frontwall 22 of the implant 10. The engaging end 28 also has restrictionmembers 47 and 49 to restrict the depth of penetration of the driver 30.

In use, the cap 32 is removed from the implant 10 and autogenous bonematerial is inserted into the hollow portion of the implant 10. The capis then replaced. Various methods of packing the implant 10 with theautogenous bon e material may be used to obtain a completely packedimplant 10.

Referring to FIGS. 4, 4a, 5 and 5a, the method of inserting the implantis shown. The threaded end 46 of the internal rod 42 of the drivingmember 30 is attached to the threaded opening 26 of the implant 10 byturning of the knob 44. Once the engaging end 28 is in place, thefitting of the extended portion 48 into the depressed portion 24prevents movement of the implant 10 in relationship to the drivingmember 30.

The implant is then placed at the entrance to the disc space between thetwo adjacent vertebrae V. The knob 44 is then tapped with hammer Hsufficiently hard enough to drive the implant 10 into the disc space.The restriction members 47 and 49 which are wider than the disc space,prevent over penetration of the implant.

The size of the implant 10 is substantially the same size as the discspace that it is replacing and thus will be larger or smaller dependingon the disc space in which it is to be used.

Referring to FIGS. 4A and 5 the implant 10 is shown in place in the discspace after removal of the driving member once the implant was insertedin place.

The autogenous bone material that was packed within the hollow portionof the implant 10 serves to promote bone ingrowth between the implantand the adjacent vertebrae. Once the bone ingrowth occurs, the implant10 will be a permanent fixture preventing dislodgement of the implant aswell as preventing any movement between the adjacent vertebrae.

Referring to FIG. 6 an alternative embodiment of the implant isdisclosed. The implant 61 comprises a substantially rectangular memberhaving a series of ridges 62 on the upper and lower surfaces of theimplant 60. One or more grooves 64 are placed on the upper and lowersurfaces as well. As indicated in FIG. 6, a series of such implants 61are used as the interbody spinal implant, each placed closely adjacentone another to approximate the size of the removed disc. A series ofmicro sized openings 63 perforate the implant 61, to promote boneingrowth.

The implant of FIG. 6 is inserted as follows: the disc is substantiallyremoved by conventional means. The implants 61 are then inserted in theintervertebral space between the two vertebrae.

The size of the implant 61 of FIG. 6 is approximately 26 millimeters inlength and is wide enough so that four of them will substantially fillthe intervertebral space, depending on which vertebras are fused.

In FIG. 6a a "bullet nosed" implant 67 having a open front portion 69 tofacilitate insertion of implant 67 is shown.

Referring to FIGS. 7 and 7a alternative embodiments of the implant 61 ofFIG. 6 is shown in place between two vertebrae V.

In FIG. 7 the implant 70 is shown with the ridges 62 shown in the formof teeth facing the anterior. These ridges serve to prevent the implant60 from `walking` out of the space between the vertebrae, functioning asratchetings to prevent backward movement of the implant.

In FIG. 7a an embodiment of the implant 70 of FIG. 6 is shown havingopposed ridges 72 and 74. This serves to maintain the alignment of thevertebrae when the two vertebrae V are improperly aligned with respectto one another.

Referring to FIG. 8 an adjustable implant 81 having means for adjustingthe width of the implant 81 is shown. The implant 81 comprises a lowermember 82 and an upper member 84 which when fitted together form anessentially rectangular implant. The upper member 84 and the lowermember 82 have hollow portions that face one another and receive taperedwedges 86 and 88 that fit within the hollow portion of the upper andlower members 82 and 84. The wedges 82 and 84 are such that at theirlarge and they are higher than the combined hollow space between theupper and lower members 84 and 82, and shallower at the other end thanthe hollow space between the upper and lower members.

The wedges 86 and 88 have a central threaded opening 90 and 92 inalignment with each other for receiving threaded screw 94. Deformableburrs 95 on the head 98 of the screw 94 are used for locking the screwin place. The implant has a series of holes 100 throughout the body ofthe implant to assist in the ingrowth process.

Referring to FIGS. 9 through 11 the expandable implant 81 is shownpositioned between the two vertebrae V. In FIG. 10 the expandableimplant 81 is illustrated in its contracted position. The wedges 86 and88 abutt the interior sloped surfaces 104 of the upper and lower members82 and 84.

As the screw 94 is turned, as shown in FIG. 11, the wedges 86 and 88 aredrawn together, and the sloped portions of the wedges force the uppermember 82 away from the lower member 84. Once the screw 94 has beenturned sufficiently, the screw head 98 is hit, causing the deformableburrs to be crimped so as to prevent the reverse rotation of the screw94.

In FIG. 12, another alternative embodiment of the expandable implant 81is illustrated with spike projections 106 extending from the top andbottom members to dig into the vertebrae and assist in maintaining it inplace.

In use, the disc is removed, and the implant 81 is placed between thevertebrae. The screw 94 is then turned expanding the implant. In thepreferred embodiment, the width is from 8 millimeters to 18 millimeters.

Referring to FIGS. 13 and 14, another alternative embodiment of theinvention is shown in which the implant 200 comprises a rectangularhollow member having a slightly tapered forward section 202. Theoristssection, shown in FIG. 14, shows the rectangular configuration of theimplant.

In use of the implant the interior of the implant is filled with a pastemade of autogenous bone, and inserted in the place of the former disc.The strength of the material used to make the implant is such that, eventhough it is substantially hollow, it does have sufficient strength towithstand the forces of the vertebrae compressing the implant.

Referring to FIGS. 15-17, another alternative embodiment is shown inwhich the implant has movable projections which are movable from a firstposition within the implant to a second position extending outside ofthe implant.

The implant 300 is of a generally rectangular configuration. The topsurface 302 and the bottom surface 304 of the implant have slots 306 forpermitting pivotal member 307 having spikes 308 at their ends to projectthrough said slots 306. The spikes 308 are pinned at one end 310 withinthe implant 300.

Opposing wedge shaped members 312 and 314 having a central threadedopening 316 for receiving a threaded screw 318 having a head 320 and aslot 322. The wedges are facing each other so that upon turning of thescrew will draw the two wedges together, causing the wedges to cause thespikes 308 to pivot about their end 310 and cause the spikes to projectout of the implant through the aligned slots 306. The depressions 329 inthe pivotal member 307 engage the wedges 314 and 312 to lock the pivotalmembers 307 in place. A series of holes 324 for promoting bone ingrowthand fusion are provided in the implant 300.

In use, after the removal of the disc material, the implants with thespikes 308 in their withdrawn position, are inserted into the discspace. Then the screw 318 is turned until the spikes 308 are forced toenter the vertebrae material, as shown in FIG. 17. The implant 300 isthus held firmly in place.

These implants have a surface configuration so as to induce boneingrowth through the implant, and into the wall of the vertebrae ineffect inducing fusion from one vertebrae V to the other, therebyeventually making the implant itself superfluous as the bone would dothe work.

The implant itself, because of its being made of stronger material thanbone, would provide structural support to the two vertebrae whileawaiting bone ingrowth. Once the bone ingrowth occurred, however, theimplant would be firmly and permanently fixed in place.

While the invention has been described with regards to the preferredembodiment and a number of alternative embodiments, it is recognizedthat other embodiments of the present invention may be devised whichwould not depart from the scope of the present invention.

What is claimed is:
 1. An implant for fusion of two adjacent vertebraein the human spine after removal of disc material between endplates ofthe adjacent vertebrae, said implant comprising:upper and lower wallsand opposite side walls between said upper and lower walls, said upperand lower walls having opposite surfaces configured to bear against andsupport a substantial portion of the endplates of the adjacentvertebrae, said implant having a plurality of openings therethroughdefined in at least said upper and lower walls, said openings beingsized to permit fusion bone growth in continuity through said implantbetween the vertebral endplates, said implant having a heightsubstantially equal to the height of the space created by the removal ofdisc material from between the adjacent vertebrae and sized and shapedto be wholly contained within the space.
 2. The implant of claim 1further comprising:a front wall and an opposite rear wall disposedbetween said upper and lower walls and said side walls.
 3. The implantof claim 2, wherein said implant has a depth between said from wall andsaid rear wall, said depth being substantially the same as the depthbetween the adjacent vertebrae of the space created by removal of discmaterial.
 4. The implant of claim 2, wherein said front wall is curvedfrom one of said side walls to the other.
 5. The implant of claim 4,wherein said front wall is convexly curved.
 6. The implant of claim 2,wherein at least a portion of said rear wall is tapered to facilitateinsertion of said implants to the disc space.
 7. The implant of claim 2,wherein said rear wall is curved from one of said side walls to theother.
 8. The implant of claim 2, wherein said front wall includesdriving engaging means for engaging a driving instrument for placingsaid implant within the disc space between the adjacent vertebrae. 9.The implant of claim 8, wherein said driving engaging means includes adepression defined in said rear wall.
 10. The implant of claim 2 whereinat least one of said front wall and said rear wall includes a pluralityof openings therethrough.
 11. The implant of claim 2, wherein said sidewalls are rounded adjacent said front wall for facilitating insertion ofsaid implant.
 12. The implant of claim 2, wherein said walls define aninterior chamber for containing fusion bone growth material.
 13. Theimplant of claim 12, wherein said upper wall defines an access openingtherethrough communicating with said interior chamber, said accessopening being substantially larger than any of said plurality ofopenings.
 14. The implant of claim 13, further comprising a cap sized toengage and close said access opening.
 15. The implant of claim 14,wherein said cap defines a number of openings therethrough incommunication with said interior chamber when said cap closes saidaccess opening.
 16. The implant of claim 12, wherein at least one ofsaid plurality of openings in each of said upper and lower wallscommunicates with said interior chamber.
 17. The implant of claim 1,wherein said rear wall is convexly curved.
 18. The implant of claim 1,wherein said implant has a width between said side wall, said widthbeing substantially equal to the transverse width of the space createdby the removed disc material.
 19. The implant of claim 1, wherein saidimplant has a width between said side walls, said width being greaterthan said height of said implant.
 20. The implant of claim 1, whereinsaid implant has a width between said side walls, said width being lessthan said height of said implant.
 21. The implant of claim 1, whereinsaid side walls are flat and are substantially parallel to each other.22. The implant of claim 1, wherein said side walls include openingsdefined therethrough.
 23. The implant of claim 1, wherein at least someof said plurality of openings in said upper and lower walls form anumber of channels through said implant.
 24. The implant of claim 1,wherein said implant is substantially rectangular.
 25. The implant ofclaim 1, wherein said implant is made at least in part of a metalsuitable for surgical implantation.
 26. The implant of claim 1, whereinat least some of said plurality of openings have a diameter ofapproximately 1 mm-3 mm.
 27. The implant of claim 1, wherein at least aportion of said walls is treated to promote bone ingrowth.
 28. Theimplant of claim 1, wherein at least one of said upper and lower wallsincludes bone engaging means for engaging said implant to at least oneof the adjacent vertebrae while fusion occurs.
 29. The implant of claim28, wherein said bone engaging means includes an irregular surface. 30.The implant of claim 29, wherein said irregular surface includes aplurality of ridges.
 31. The implant of claim 30, wherein said ridgesare ratchetings facing the same direction to prevent expulsion of saidimplant in said same direction.
 32. The implant of claim 30, whereinsaid bone engaging means includes ridges defined on both said top andsaid bottom walls.
 33. The implant of claim 33, wherein said ridges onat least one of said top and bottom surfaces are ratchetings facing onedirection to prevent expulsion of said implant in said one direction.34. The implant of claim 33, wherein said ridges on said top surface areratchetings facing said one direction and said ridges on said bottomsurface are ratchetings facing a direction opposite said one direction.35. The implant of claim 1, wherein said implant includes a rounded endbetween said upper and lower walls to facilitate insertion of saidimplant between the adjacent vertebrae.
 36. A spinal implant for fusionof two adjacent vertebrae in a human after removal of disc materialbetween vertebral endplates of the adjacent vertebrae, said implantcomprising:upper and lower walls a front wall and an opposite rear wallbetween said upper and lower walls and side walls between said upper andlower walls and said front and rear walls, said implant having a heightbetween said upper and lower walls substantially equal to the height ofthe space created by removal of disc material between the adjacentvertebrae and sized and shaped to be wholly contained within the space,a plurality of openings defined in each of at least said upper and lowerwalls, said upper and lower walls defining substantially planar surfacesconfigured to bear against the vertebral endplates, and a hollowinterior chamber enclosed by said walls in communication with saidplurality of openings and accessible through an access opening definedin one of said walls, said interior chamber being larger than any ofsaid plurality of openings and sized to contain fusion promotingmaterial, said plurality of openings sized to permit fusion bone growthin continuity through said implant between the endplates of the adjacentvertebrae and with the fusion promoting material that may be containedwithin said interior chamber.
 37. The spinal implant of claim 36,wherein said access opening is larger than any of said plurality ofopenings.
 38. The implant of claim 10 in which said plurality ofopenings are smaller than said access opening.
 39. The spinal implant ofclaim 36, further comprising a cap sized to engage and close said accessopening.
 40. The spinal implant of claim 39 wherein said cap defines anumber of openings therethrough in communication with said interiorchamber when said cap closes said access opening.
 41. The spinal implantof claim 39 further comprising a threaded engagement between said capand said access opening.
 42. The spinal implant of claim 41 wherein saidcap defines a tool opening for receiving a tool to thread said cap intosaid access opening.
 43. An interspace fusion implant for fusion of twoadjacent vertebrae in the human spine after removal of disc materialbetween endplates of the adjacent vertebrae said implant comprising:aload bearing structure formed of a material that is stronger than bone,said structure sized and shaped to be wholly contained within the spaceleft after removal of the disc material and including opposite upper andlower walls having opposite surfaces configured to bear against asubstantial portion of the endplates of the adjacent vertebrae, saidload bearing structure having a height between said upper and lowerwalls that is substantially equal to the height of the space created bythe removal of the disc material; and a plurality of openings defined ineach of said upper and lower walls, said plurality of openings beingsized and arranged to permit fusion bone growth in continuity between atleast several of said plurality of openings in said upper wall and atleast several of said plurality of openings in said lower wall.
 44. Theinterspace fusion implant of claim 43, wherein said load bearingstructure further defines an interior chamber in communication with eachof said plurality of openings in each of said upper and lower walls. 45.The interspace fusion implant of claim 44, wherein:said upper walldefines an access opening therethrough in communication with saidinterior chamber; and said implant further comprises a cap for engagingand closing said access opening.
 46. The interspace fusion implant ofclaim 45, wherein said cap defines at least one opening therethrough incommunication with said interior chamber when said cap closes saidaccess opening.
 47. The interspace fusion implant of claim 43, whereinat least said opposite surfaces of said upper and lower walls aretreated with a material to promote bone ingrowth into said oppositesurfaces.
 48. The interspace fusion implant of claim 43, wherein saidload bearing structure includes opposite side walls between said upperand lower walls, each of said side walls defining a number of openingstherethrough.
 49. The interspace fusion implant of claim 43, whereinsaid load bearing structure includes opposite end walls between saidupper and lower walls, at least one of said end walls being convexlycurved.
 50. The interspace fusion implant of claim 43, wherein said loadbearing structure includes opposite end walls between said upper andlower walls, at least one of said end walls being rounded to facilitateinsertion of the implant between the adjacent vertebrae.